8 ARKIV FÖR ZOOLOGI. BAND 8. N.O 9. 



The so-called X-line, demarcating the endoskeletal ridges 

 on the dorsal side of the capsule, differs essentially from 

 that of other larvae. 



In these it is very narrow, but projects deeply into the 

 interiör of the head, and appears either as a bifurcate line 

 with the proximal 1 /a or 1 /s simple or as two lines which 

 meet at the posterior edge of the capsule in the bottom of 

 the incision. 



In the leaf miners we notice two features : Firstly, the 

 ridges are much broader, which probably compensates for 

 their having become lower on account of the dorsoventral 

 compression ; secondly, they never have a simple posterior 



Fig. 4. Head and thoracic segments of Nepticula, lateral aspect. 



portion, but meet first at the hind margin, and at that point 

 there is a tendency to form a bridge which increases in 

 length at the same råte as the ridges become more parallel 

 to each other. In Elachista (fig. 2), Nepticula (fig. 3) and 

 Gemiostoma (fig. 1), we have a series enabling us to gradually 

 follow this development; in the sap-feeders w T e find this de- 

 velopment carried to the extreme. 



b) Sap-feeders. 



The head differs from that of the tissue-feeders in several 

 essential respects. In the latter, we were able to follow how 

 the capsule became more and more deeply retracted within 

 the prothorax. In the sap-feeders, on the contrary, it is 



